The invention relates to an arrangement for transferring data between a desk top computer and a peripheral device or other data processing device, particularly, but not exclusively, portable data processing devices such as personal digital assistants and lap top computers. The invention further relates to a computer mouse mat which includes data transfer means.
There are an increasing number of portable and peripheral devices that provide a need for data transfer between them and a desk top computer. Such devices include lap top computers, personal digital assistants (PDA) communications equipment containing modems for accessing databases etc. While these devices are designed to be used mainly in a stand-alone mode for use when the user is away from a permanent location, they often need to be connected to a fixed computer system at the user""s base. For example the user may wish to download data or files from a lap top computer or PDA on to the fixed computer system.
Such a requirement gives rise to the need for simple and reliable data transfer between the devices, preferably at high speed. A number of possibilities have been proposed and implemented but they all have specific limitations. Plug and socket arrangements require standardisation between the various components which is largely been achieved. They also, however, suffer some reliability problems. The projections in the male section of a typical data connector are subject to damage by contamination, by misaligned insertions and by physical impacts (for example when dropped). The female section may also be damaged by contamination (which can be alleviated by appropriate hinged covers but at extra cost) and by misaligned insertions.
An alternative approach is wireless transfer using either radio waves or infra-red radiation. The former has regulatory restrictions which vary from country to country and which may cause problems for travellers and the latter requires line of sight between the infra red transmitter and receiver. In both cases a relatively expensive transmitter and receiver is required and the transmitter will also consume significant power, which is particular disadvantage for battery powered equipment. Simple infra-red data links also tend to have a limited speed of data transfer.
EP-A-0676710 discloses portable computing and communications devices which are connected with other typically fixed devices via the use of a capacitative data connector. Each of the two mating sections of the connector include a set of coupling plates. When the two sections are brought into contact the coupling plates form capacitors across which data signals can be passed. Circuitry driving each section of the data connector is such as to create a bi-directional signalling path, thereby providing a connection, which is functionally equivalent to an ohmic connection. Signals that are typically passed across data connectors on individual parallel leads are in the disclosed data connector serialised, passed across the connector in that form and connected back to parallel form on the other side of the connection. Each section of the connector illustratively includes a permanent magnet to draw and hold the two sections in alignment, thereby providing a connector, which is self aligning.
The connector disclosed in EP-A-0676710 overcomes some of the disadvantages disclosed above in that physical contact between the coupling plates is not made, there is a gap left to form a dielectric of the capacitor. The connector disclosed in this patent application does, however, suffer from some disadvantages in that it is a relatively expensive construction and it is necessary to accurately locate the two parts of the connector together.
It is an object of the invention to enable the transfer of data between a desk top computer and a peripheral device or other data processing device which mitigates at least some of the disadvantages of the prior art arrangement set out above.
The invention provides an arrangement for transferring data between a computer and peripheral device or other data processing device, the arrangement comprising a first pair of conductive plates connected to said computer and a second pair of conductive plates, said second pair being carried on or formed as part of a wall of the housing of said peripheral device or other data processing device, means for bringing the first and second conductive plates into close proximity so as to form a pair of capacitors: wherein for transmitting data from the computer to the peripheral device or other data processing device the computer includes means for applying the data to be transferred in the form of a differential pulse voltage to the first pair of conductive plates and the peripheral device or other data processing device includes means for detecting the differential voltage impressed on the second pair of conductive plates by that applied to the first pair of conductive plates and converting the detected differential voltage to appropriate data pulses for use by and/or storage in the peripheral device or other data processing device, and/or wherein for transmitting data from the peripheral device or other data processing device to the computer the peripheral device or other data processing device includes means for applying the data to be transferred in the form of a differential pulse voltage to the second pair of conductive plates and the computer includes means for detecting the differential voltage impressed on the first pair of conductive plates by that applied to the second pair of conductive plates and converting the detected differential voltage to the appropriate data pulses for use by and/or storage in the computer.
By this means a simple low cost data transfer between a computer and portable data processing devices can be achieved. The alignment between the first and second pairs of plates does not have to be exact and a simple placing of the second pair in proximity to the first is sufficient. The power consumption associated with infra red or radio transmitters is avoided and no costly plug and socket connectors are required.
In a first embodiment the first pair of conductive plates may be external to the computer and connected to the housing of the computer by a twisted pair of conductors or by a screened pair of conductors. In this case the first pair of conductive plates are, in effect, on a flying lead and the peripheral device or other data processing device may be placed directly on top of the first pairs of plates so that the second pair of plates is brought into proximity with the first. Alternatively, of course the first pair of plates could be placed on top of the peripheral device or other data processing device.
In a second embodiment the first pair of conductive plates is carried on or formed as part of a wall of the housing of the computer. This eliminates the potentially vulnerable flying leads but requires at least a portion of one surface, normally a horizontal upper surface, to be left uncovered to accommodate the peripheral device or other data processing device when data transfer is required. Thus it may not be possible to place a monitor on top of the computer housing if this arrangement is adopted. This has the potential disadvantage of requiring a larger desk space to accommodate the computer.
As a further optional refinement of the second embodiment the first pair of conductive plates may be surrounded by an electromagnetic shield. This reduces any problems of electromagnetic interference, which may arise during data transfer. It is also possible to use the electromagnetic shield as a means of locating the peripheral device or other data processing device with its (second) pair of conductive plates in proximity to the (first) pair of conductive plates formed on the computer.
The peripheral devices or other data processing devices may take many forms. Examples are lap top computers, personal digital assistants, modems, printers, scanners etc.
The pair of conductive plates in the peripheral device of other data processing device may be formed in many ways. Inexpensive constructions are metal foils attached by adhesives to the inside of a wall of the housing containing the device or a conductive paint sprayed on the inside of the wall of the housing.
The invention further relates to a mouse mat having formed therein two conductive plates covered by an insulating layer on which a mouse may be manoeuvred and comprising means for coupling the two conductive plates to a data transfer port of a computer.
This has the advantage that the transfer pad attached to the computer is formed in an article which is normally associated with a desk top computer and will normally be present on a desk adjacent to the computer. In addition a mouse mat will usually be kept clear of any equipment or papers to enable a mouse to be used. Consequently, for data transfer, it is merely necessary to move the mouse and replace it on the mat by the portable device.
The mouse mat may carry a printed indicator of the centre line between the two conductive plates. This enables the portable equipment to be located easily into a position where its conductive plates are aligned with those in the mouse mat, and is particularly useful where the portable equipment is very different in size from the mat.
The coupling means may comprise a pair of conductors, each pair having one end connected to a respective one of the plates and the other end connected to one part of a plug and socket arrangement. The other part of which is mounted on the computer.
This gives an arrangement of a mouse mat with a flying lead for coupling to the computer in a manner similar to that by which a mouse is coupled to the computer. An alternative arrangement would be to have fixed pins on the perimeter of the mouse mat to which a connector was coupled.